Freight brake control valve device having improved quick service function

ABSTRACT

A freight brake control valve device having an improved quick service function achieved by providing an additional volume upstream of the quick service limiting valve with which the brake pipe fluid under pressure is equalized during the second stage of quick service to achieve an intensified secondary quick service reduction of brake pipe pressure. Further, a smooth and continuous local reduction of brake pipe pressure occurs without any time lag at the time of transition from preliminary to secondary stage quick service. In a first embodiment of the invention, an exhaust passage separate from the brake cylinder exhaust passage is provided to assure venting of this additional volume in the event the brake cylinder retainer valve is set up. In a second embodiment, the additional volume is vented via the brake cylinder exhaust passage.

BACKGROUND OF THE INVENTION

The present invention is related to railway car freight brake controlvalve devices and particularly to the quick service function provided bythese control valve devices for effecting a local venting of the trainbrake pipe air at each car in order to propagate the brake pipe pressurereduction through the train when a brake application is initiated.

Quick service venting of brake pipe pressure is achieved, as a two-stageoperation, in the present standard ABD and ABDW freight brake controlvalve devices. During the first stage, known as preliminary quickservice, initial movement of the service piston slide valve from releaseposition toward service position, in response to a train line reductionof brake pipe pressure, establishes a communication between the carbrake pipe and a quick service bulb or volume that is, in turn, ventedto atmosphere via a quick service exhaust choke. A local reduction ofbrake pipe pressure is effected by this communication to supplement thetrain line reduction of brake pipe pressure at each car, therebyserially transmitting the brake application signal from one car to thenext car. In addition, this local reduction of brake pipe pressureencourages continued movement of the service piston to service positionwithout hesitation, wherein the second stage of quick service isrealized.

During this secondary stage of quick service, the service piston slidevalve cuts off brake pipe pressure from the quick service bulb andconnects the brake pipe pressure to the car brake cylinder device viathe piston valve stem of the quick service limiting valve untilapproximately 10-12 psi brake cylinder pressure is developed. With theservice piston in service position, it will be appreciated thatauxiliary reservoir pressure is also connected to the car brake cylinderdevice concurrently with the brake pipe pressure during this secondarystage of quick service.

It has been found that, due to the relatively high pressure differentialbetween brake pipe and auxiliary reservoir created by the first stagequick service reduction of brake pipe pressure, the degree of servicepiston movement into service position is such that maximum flow capacityis established at the service piston graduating valve port connectingauxiliary reservoir pressure to the brake cylinder device. The flowcapacity of auxiliary reservoir pressure via this port openingmomentarily exceeds the downstream flow capacity to the brake cylinder,thereby creating a short term back pressure surge or pressure pulse inthe brake cylinder feedback passage to the quick service limiting valvedevice. Consequently, the brake cylinder pressure signal at the quickservice limiting valve control piston reaches the cut-off value of 10-12psi before the actual brake cylinder pressure builds up this value.Accordingly, the quick service limiting valve is operated to interruptthe connection of brake pipe pressure to the brake cylinder deviceprematurely, and following dissipation of the back pressure pulse,re-establishes the brake pipe connection to the brake cylinder device.

Ideally, a smooth and continuous transition of the local quick servicebrake pipe pressure reduction should occur between the first stagepreliminary quick service activity and the secondary stage of quickservice. Due, at least in part, to this premature operation of the quickservice limiting valve, however, a disruption occurs in the local quickservice reduction of brake pipe pressure during the transition betweenthe preliminary and secondary stages of quick service. This disruptionis indicated by a time lag C, in the graph of FIG. 1, wherein curve Arepresents the secondary quick service reduction of brake pipe pressureachieved in accordance with the present invention and curve B representsthe secondary quick service reduction of brake pipe pressure achieved inthe standard ABD and ABDW control valve devices. As can be seen fromthis graph, during the secondary stage of quick service, curve B isdisplaced with respect to a curve D representing the brake pipe pressurereduction during preliminary quick service, so that within time periodC, no local reduction of brake pipe pressure occurs.

OBJECTS OF THE INVENTION

It is, therefore, the object of the present invention to provide afreight brake control valve device having an improved quick servicefunction.

A further object of the invention is to decrease the time required toachieve a given reduction of brake pipe pressure by intensifying thesecond stage of quick service activity.

A still further object of the invention is to assure a local reductionof brake pipe pressure during the second stage of quick serviceirrespective of premature closure of the quick service limiting valveand/or retainer valve operation.

Briefly, the foregoing objectives are achieved in the present inventionby providing a secondary quick service bulb or volume in the brake pipepassage between the service piston slide valve and quick servicelimiting valve to provide a quick service reduction of brake pipepressure during such time as the quick service limiting valve device isprematurely actuated to cut-off position due to the momentary pressuresurge experienced during transition from preliminary quick service tosecondary quick service, as the service piston moves from release toservice position. During brake release, the secondary quick service bulbis vented either via the brake cylinder exhaust passage or via aseparate exhaust passage.

The foregoing objects and other advantages of the invention will becomeapparent from the following more detailed explanation when taken inconjunction with the accompanying drawings in which:

FIG. 1 is a graph showing the quick service brake pipe pressurereduction curve obtained with the present standard ABD and ABDW typefreight brake control valve devices and a brake pipe pressure reductioncurve achieved in accordance with the present invention;

FIG. 2 is a fragmentary diagrammatic view of an ABD/ABDW control valveservice portion shown in release position and modified according to oneembodiment of the present invention; and

FIG. 3 is a fragmentary diagrammatic view of an ABD/ABDW type controlvalve service portion shown in release position and modified accordingto another embodiment of the present invention.

DESCRIPTION AND OPERATION

In the embodiment of FIG. 2, there is shown a service portion 2 of afreight brake control valve device of the ABD/ABDW type. As is wellknown to those skilled in the railway braking art, service portion 2includes a service piston 11 having a slide valve 13 and a graduatingvalve 12 that cooperate to control the supply, lap, and exhaust of airpressure effective at the brake cylinder device(s) 3 of a railwayvehicle freight car, in accordance with pressure variation of thecompressed air carried in the car brake pipe 1. Service portion 2 alsoincludes a preliminary quick service bulb or volume 4, a quick servicelimiting valve 6, and a secondary quick service bulb or volume 7.

In the release position shown, the compressed air carried in brake pipe1 is connected via passage b1 to chamber B on the face of the servicediaphragm piston 11 and to the service slide valve seat. The brake pipeair is also connected via a charging choke 26 and passage b2 to theslide valve seat, from where a choked orifice k in the slide valvecommunicates with passage b2 to charge a chamber Y on the underside ofservice piston 11. A passage a1 is connected from chamber Y to theauxiliary reservoir 5, which is thus charged to the pressure carried inbrake pipe 1. With brake pipe pressure effective in chamber B andauxiliary reservoir pressure effective in chamber Y charged to the samepressure, a spring 18 establishes release position of service piston 11,in which brake cylinder device(s) 3 is connected to atmosphere viapassages C, C1, C5, slide valve port t, exhaust passage 10, exhaustchoke 25, and retainer valve 9. A slide valve port g connects thesecondary quick service volume 7 to atmosphere via passage b5 andanother exhaust passage 8.

With the brake equipment charged to brake pipe pressure as previouslydescribed, a service brake application is made at the brake valve byreducing the brake pipe pressure at a controlled rate.

Brake pipe pressure in chamber B on the face of the service diaphragmpiston 11 is thus reduced and the pressure in chamber Y deflects thediaphragm piston 11, moving it and the graduating valve 12 upward. Theauxiliary reservoir charging choke 26 creates the foregoing differentialby preventing auxiliary reservoir air in chamber Y below the servicediaphragm piston from flowing back into brake pipe as fast as the brakepipe is reducing in chamber B above the service diaphragm piston.

The stabilizing spring guide 14 engages the end of the service slidevalve 13 and further movement of the diaphragm piston and graduatingvalve 12 toward service position compresses the stabilizing spring 16.As its name indicates, the stabilizing spring offers a predeterminedresistance to diaphragm piston and graduating valve movement so thatundesired quick service applications will not be caused by smallfluctuations in brake pipe pressure. During this initial diaphragmpiston movement, the attached service graduating valve 12 blanks port kin the slide valve, cutting off chamber Y and auxiliary reservoir frombrake pipe charging passage b2. It also uncovers port d in the slidevalve 13 connecting auxiliary reservoir air to the slide valve seat.After the stabilizing spring is compressed, cavity h in the graduatingvalve connects ports h1 and h2 through the slide valve, permitting brakepipe air to flow from passage b1 to passage b6 and the preliminary quickservice volume 4. This produces a local reduction of brake pipe pressureby allowing brake pipe air to flow into the preliminary quick servicevolume. The reduction is transmitted in rapid wave action serially fromcar to car; each ABD/ABDW control valve in turn acts in repeatersequence to the adjacent valve to develop prompt starting of brakeapplication on all cars in the train.

The preliminary quick service volume 4 is permanently connected toatmosphere through a quick service exhaust choke 39. By this means, abrake pipe pressure buildup develops in the preliminary quick servicevolume. This local reduction of brake pipe pressure continues untilsufficient pressure differential develops across the service diaphragmpiston to move the service slide valve to service position.

As the service piston moves upwardly to service position, the serviceslide valve is moved upwardly on its seat, port h2 moving out ofregistry with port b1 and cutting off flow of brake pipe air frompassage b1 to passage b6, thereby terminating the preliminary quickservice activity. The preliminary quick service volume pressure issubsequently dissipated through exhaust choke 39.

In service position, of service piston 11, cavity d in slide valve 13registers with passage c5 at the slide valve seat, connecting auxiliaryreservoir air to brake cylinder device(s) 3 via passages c5, c1 and c.The air in passage c5 is also connected to a feedback passage c9 leadingto chamber F of the quick service limiting valve 6. The force of thisair acting on the upper side of the quick service limiting valve controlpiston 19 acts against the force exerted by bias spring 20 to actuatethe control piston when approximately 10-12 psi brake cylinder pressuredevelops. At the same time, slide valve port g moves out of registrywith exhaust passage 8 and registers passage b1 with passage b5. Priorto actuation of control piston 19, brake pipe air in passage b1 is thusconnected via slide valve port g and passage b5 to a groove 33 in thestem of control piston 19, which is registered with chamber F andfeedback passage c9 to feed brake pipe pressure to brake cylinderdevice(s) 3 during secondary quick service. Due to the relatively largepressure differential created between the brake pipe and auxiliaryreservoir pressures acting across service piston 11, as a result of thepreliminary quick service activity, however, the service piston ispositioned to establish full registry of slide valve port d with passagec5, thereby providing a rapid influx of air from auxiliary reservoir 5to the brake cylinder supply passages, the flow capacity of which isrestricted by chokes (not shown) in these passages c1 and c downstreamof the slide valve. Consequently, a momentary back pressure surge isdeveloped in feedback passage c9, which is reflected at chamber F of thequick service limiting valve 6. This back pressure surge causes a falsebrake cylinder pressure signal to be effective in chamber F in the formof a momentary high amplitude pressure surge or pulse that exceeds theopposing bias force exerted by spring 20. Consequently, piston 19 can beprematurely and inappropriately actuated to its cut-off position inwhich the secondary quick service flow of brake pipe pressure to brakecylinder(s) 3 via groove 33 in the piston stem is interrupted. Sincesecondary quick service volume 7 is located upstream of the quickservice limiting valve, however, a local reduction of brake pipepressure is assured by equalization into the previously vented secondaryquick service volume 7 to provide an initial phase of the secondaryquick service reduction of brake pipe pressure, as represented by curveA' in the graph of FIG. 1.

It will be appreciated, therefore, that during the brief time periodthat quick service limiting valve 6 may be prematurely actuated due tothe momentary pressure surge during the transition between preliminaryand secondary quick service, as previously discussed, this connection ofbrake pipe air to secondary quick service volume 7 will provide acontinuing local reduction of brake pipe pressure without anysubstantial interruption, thereby substantially eliminating the time lagnoted at c in the graph of FIG. 1.

Following dissipation of the momentary false back pressure signal orpressure pulse effective in chamber F, spring 20 will become effectiveto reset control piston 19 and reestablish quick service flow of brakepipe pressure to brake cylinder(s) 3 until the brake cylinder pressureeffective in chamber F builds up to 10-12 psi.

During this final phase of secondary quick service, as represented bycurve A" in the graph of FIG. 1, limiting valve 6 is effective toreestablish flow of brake pipe pressure to brake cylinder(s) 3 inconjunction with the continuing flow of brake pipe pressure to volume 7.In this manner, an intensified secondary quick service function isachieved, in which the local rate of brake pipe pressure reduction, asrepresented by the slope of curve A', A" in FIG. 1, is greater than thesecondary stage quick service reduction of brake pipe pressure generatedin the standard ABD/ABDW control valve device, as represented by theslope of curve B. Curve A', A" is not only steeper than curve B, butalso occurs without any significant hesitation or time lag, thusproducing a faster propagation of the trainline brake pipe pressurereduction and accordingly a faster response of the train brakes.

When this pressure in chamber F and brake cylinder device(s) 3 issufficient to overcome the bias force exerted by spring 20, controlpiston 19 will be appropriately actuated downwardly to a cut-offposition in which groove 34 in the stem of control piston 19 isolatespassage b5 from chamber F and passage c9 to terminate the second stageof quick service activity. In this manner, a minimum brake cylinderpressure of approximately 10-12 psi is assured in response to a brakepipe pressure reduction.

Upon subsequently increasing brake pipe pressure to effect a brakerelease in the usual, well-known manner, service piston 11 assumes itsrelease position, as shown, in which slide valve port t establishescommunication between brake cylinder passage c5 and exhaust passage 10to release the brake cylinder pressure via retainer valve 9. At the sametime, slide valve port g connects passage b5 with the secondary quickservice exhaust passage 8. This provides an alternate exhaust path viawhich passage b5 and the secondary quick service volume 7 are ventedduring each brake release, in the event quick service limiting valve 6is unable to reset due to retainer valve 9 being set to retain brakecylinder pressure at a high enough value to overcome spring 20. Thisassures that, even though the quick service limiting valve piston 19 isunable to reset, the secondary quick service volume will be vented viathe secondary quick service exhaust passage 8 each time a brakeapplication is released to assure secondary quick service activityduring a subsequent brake application, by equalization of brake pipepressure with the previously vented secondary quick service volume 7. Inthis manner, a brake assurance feature is provided when employingretainer valves.

The embodiment of the invention shown in FIG. 3 differs from the FIG. 2embodiment only in that secondary quick service volume 7 is vented toatmosphere via the brake cylinder exhaust passage 10, instead of via theseparate exhaust passage 8 of FIG. 2. This is achieved by connecting abranch passage b5a of passage b5 in the service portion body 2 to theface of slide valve 13 and adding a passage p of port t that registerswith passage b5a in release position of service piston 11.

The preliminary and secondary quick service functions are achieved inthe same manner as disclosed in the embodiment of FIG. 1. It will beappreciated that, upon movement of service piston 11 from preliminaryquick service position to service application position, in whichposition secondary quick service is achieved, slide valve passage pmoves out of registry with passage b5a, thereby cutting off the exhaustconnection of the secondary quick service volume prior to the secondaryquick service connection of passages b1 and b5 being established viaport g. Accordingly, brake pipe pressure is connected to secondary quickservice volume 7 to effect a local quick service reduction of brake pipepressure, in addition to the local quick service reduction of brake pipepressure via the quick service limiting valve 6. In this manner, anintensified secondary quick service function is achieved, in which therate of local brake pipe pressure reduction, as represented by the slopeof curve A', A" of FIG. 1, approaches the rate of brake pipe pressurereduction achieved during preliminary quick service.

Moreover, in the event quick service limiting valve 6 is inappropriatelyactuated due to the momentary pressure surge during transition betweenpreliminary and secondary quick service, as previously discussed, thisconnection of brake pipe air to secondary quick service volume 7 willprovide a continuing local reduction of brake pipe pressure without anysignificant interruption, thereby substantially eliminating the lagnoted at C in the graph of FIG. 1. In accordance with the presentinvention, therefore, relative to the embodiment of FIG. 3, curve A', A"will not only be steeper than curve B, but will occur with substantiallyno hesitation or time lag, thus producing a faster propagation of thetrainline brake pipe pressure reduction and accordingly a fasterresponse of the train brakes.

Upon releasing the brake application, movement of service piston 11 torelease position locates slide valve 13 such that slide valve port g isout of registry with passage b1, port t establishes registry withexhaust passage 10, and passage p of port t is registered with passageb5a. This assures that, in the event retainer valve 6 is set up in thepressure retention position, so as to retain 20 psi brake cylinderpressure, for example, and thus prevent quick service limiting valve 6from resetting, the pressure in secondary quick service volume 7 will beexhausted via passage b5, passage b5a, slide valve passage p and port t,and exhaust passage 10. While the pressure in volume 7 will only beexhausted to the pressure set by retainer valve 6, sufficient pressuredifferential between the trapped pressure in volume 7 and the effectivebrake pipe pressure, (particularly following a minimum service brakeapplication) will exist to assure secondary quick service activity on asubsequent brake application, thereby providing a brake assurancefeature when employing retainer valves.

We claim:
 1. For controlling the brakes on a railway car having a brakepipe normally charged with fluid at a certain chosen pressure, anauxiliary reservoir charged with fluid under pressure from said brakepipe, and a fluid pressure actuated brake cylinder device, there isprovided a brake control valve device comprising:(a) a service pistonabutment subject opposingly to said brake pipe fluid under pressure andsaid auxiliary reservoir fluid under pressure; (b) a supply passageconnected to said brake cylinder device; (c) a preliminary quick servicevolume; (d) a secondary quick service volume; (e) valve means carried bysaid service piston abutment for establishing a preliminary quickservice connection of fluid pressure from said brake pipe to saidpreliminary quick service volume during initial movement of said servicepiston from a release position to a service position in response to areduction of said brake pipe fluid under pressure relative to saidauxiliary reservoir fluid under pressure, and during subsequentmovement, cutting off said preliminary quick service connection, whileconcurrently establishing a service connection of said auxiliaryreservoir fluid under pressure to said supply passage, and a secondaryquick service connection of said brake pipe fluid under pressure to saidsupply passage and to said secondary quick service volume; and (f) quickservice limiting valve means downstream of said secondary quick servicevolume operative in response to said brake cylinder fluid under pressureeffective in said supply passage exceeding a first predetermined valuefor interrupting flow of said brake pipe fluid under pressure to saidsupply passage via said secondary quick service connection.
 2. A brakecontrol valve device as recited in claim 1, further comprising:(a) afirst exhaust passage via which said supply passage is vented toatmosphere in said release position of said service valve to releasefluid under pressure from said brake cylinder device; (b) retainer valvemeans in said exhaust passage for preventing said brake cylinder fluidunder pressure from exhausting to a value less than a secondpredetermined value, said second predetermined value being at least asgreat as said first predetermined value, whereby said quick servicelimiting valve is maintained in said actuated position; (c) a secondexhaust passage; and (d) said valve means further connecting saidsecondary quick service volume to said second exhaust passage in saidrelease position of said service piston.
 3. A brake control valve deviceas recited in claim 2, wherein said preliminary quick service volume ispermanently vented to atmosphere.
 4. A brake control valve device asrecited in claim 1, further comprising:(a) a first exhaust passage viawhich said supply passage is vented to atmosphere in said releaseposition of said service valve to release fluid under pressure from saidbrake cylinder device; (b) retainer valve means in said exhaust passagefor preventing said brake cylinder fluid under pressure from exhaustingto a value less than a second predetermined value, said secondpredetermined value being at least as great as said first predeterminedvalue, whereby said quick service limiting valve is maintained in saidactuated position; and (c) said valve means further connecting saidsecondary quick service volume to said first exhaust passage in saidrelease position of said service piston.
 5. A brake control valve deviceas recited in claim 4, wherein said preliminary quick service volume ispermanently vented to atmosphere.